Free
Correspondence  |   October 1995
Carbon Dioxide Reactivity and Cerebral Ischemia: Is the Cortical Somatosensory Evoked Potential a Sensitive Detector of Cerebral Ischemia?
Author Notes
  • Abteilung fur Anaesthesiologie und Operative Intensivmedizin, Justus-Liebig-Universitat, Klinikstrasse 29, 35385 Giessen, Germany.
Article Information
Correspondence
Correspondence   |   October 1995
Carbon Dioxide Reactivity and Cerebral Ischemia: Is the Cortical Somatosensory Evoked Potential a Sensitive Detector of Cerebral Ischemia?
Anesthesiology 10 1995, Vol.83, 890-891.. doi:
Anesthesiology 10 1995, Vol.83, 890-891.. doi:
In Reply:--Although Mahla and Sulek suggest that the "ideal" monitor to detect cerebral ischemia during carotid endarterectomy has not been found, there are convincing data from human studies that somatosensory evoked potentials (SEPs) after median nerve stimulation are highly specific and sensitive to detect cerebral ischemia during carotid surgery, [1-3] which, in our opinion, may make SEP monitoring superior to electroencephalography (EEG) for three reasons. First, EEG monitoring appears to be "oversensitive" as ischemic changes will occur in up to 40% intraoperatively, [4,5] whereas new postoperative neurologic deficits even using a "no shunt" regimen will not exceed 8-10% in experienced centers. The latter percentage is remarkably close to the findings of our group [1,6,7] that SEP changes indicating ischemia (amplitude reduction > 50%, central conduction time (CCT) prolongation > 20%) will occur in 10-15%. Thus, it is not surprising that Kearse et al. [8] found SEP much less sensitive when compared with the high incidence of ischemic EEG changes (43%) in their study. Second, EEG monitoring methods may not be sensitive enough to detect ischemia (false negative) in patients suffering from preoperative neurologic symptoms, [9,10] whereas false-negative SEP findings in carotid surgery have been reported in only one study. [11] Third, EEG monitoring relies on the detection of multiple patterns that, in the absence of computer-aided analysis, are difficult to quantify and require an experienced neurophysiologist. SEP recordings, in contrast, allows the identification of ischemia using only few quantitative parameters (latency and/or CCT, amplitude).
However, in the absence of carefully controlled clinical studies demonstrating the superiority of one monitoring method, EEG remains undoubtedly an appropriate means to detect cerebral ischemia during carotid surgery. We agree with Mahla and Sulek.
Achim Thiel, M.D., Abteilung fur Anaesthesiologie und Operative Intensivmedizin, Justus-Liebig-Universitat, Klinikstrasse 29, 35385 Giessen, Germany
(Accepted for publication July 27, 1995.)
REFERENCES
Russ W, Fraedrich G, Hehrlein FW, Hempelmann G: Intraoperative somatosensory evoked potentials as a prognostic factor of neurologic state after carotid endarterectomy. Thorac Cardiovasc Surg 33:392-396, 1985.
Lam AM, Manninen PH, Ferguson GG, Nantau W: Monitoring electrophysiologic function during carotid endarterectomy: A comparison of somatosensory evoked potentials and conventional electroencephalogram. ANESTHESIOLOGY 75:15-21, 1991.
Schweiger H, Kamp HD, Dinkel M: Somatosensory-evoked potentials during carotid artery surgery: Experience in 400 operations. Surgery 109:602-609, 1991.
Spackman TN, Faust RJ, Cucciara RF, Sharbrough FW: A comparison of the Lifescan EEG monitor with EEG and cerebral blood flow for detection of cerebral ischemia. ANESTHESIOLOGY 63:A187, 1985.
Sundt TM, Sharbrough FW, Piepgras DG, Kearns TP, Messick JM, O'Fallon WM: Correlation of cerebral blood flow and electroencephalographic changes during carotid endarterectomy. Mayo Clin Proc 56:533-543, 1981.
Thiel A, Zickmann B, Stertmann WA, Wyderka T, Hempelmann G: Cerebrovascular carbon dioxide reactivity in carotid artery disease: Relation to intraoperative cerebral monitoring results in 100 carotid endarterectomies. ANESTHESIOLOGY 82:655-661, 1995.
Thiel A, Russ W, Zeiler D, Dapper F, Hempelmann G: Transcranial Doppler sonography and somatosensory evoked potential monitoring in carotid surgery. Eur J Vasc Surg 4:597-602, 1990.
Kearse LA, Brown EN, McPeck K: Somatosensory evoked potentials sensitivity relative to electroencephalography for cerebral ischemia during carotid endarterectomy. Stroke 23:498-505, 1992.
Rampil IJ, Holzer JA, Quest DO, Rosenbaum SH, Correll JW: Prognostic value of computerized EEG analysis during carotid endarterectomy. Anesth Analg 62:186-192, 1983.
Silbert BS, Kluger R, Cronin KD, Koumoundouros E: The processed electroencephalogram may not detect neurologic ischemia during carotid endarterectomy. ANESTHESIOLOGY 70:356-358, 1989.
De Vleeschauer P, Horsch S, Matamoros R: Monitoring of somatosensory evoked potentials in carotid surgery: Results, usefulness and limitations of the method. Ann Vasc Surg 2:63-68, 1988.